One of the most common questions at veterinary hospitals is "Why does my dog eat grass?" Urban legend states pets eat grass because they "know" they are sick and need to vomit or that the pet is aware of some dietary deficiency. Of course, in spring and summer, we see a spike of grass ingestion as our yards and play areas become freshly green and viable.

To test these hypotheses, veterinarians at the University of California at Davis School of Veterinary Medicine designed surveys to question pet owners about their pets' grass eating habits.

An initial survey of owners of healthy dogs found 80 percent of dogs with access to plants had eaten grass or other plants. The study also surveyed dog owners about their dogs' plants eating habits and the dogs' diet and gathered information about breed, sex, neuter status and age.

More than 3,000 owners responded to an extensive online survey. Of these, almost 1,600 surveys were considered to be usable. About 68 percent of responders stated their dogs ate plants daily or weekly.

Only 8 percent of dogs showed signs of illness prior to ingesting plant material and 22 percent of dogs vomited after eating plants.

The survey also showed that those dogs showing signs of illness before eating plants were more likely to vomit than those who appeared healthy beforehand.

Finally, younger dogs were more likely to eat plants but less likely to appear ill prior to eating or vomit after eating the plant material.

The veterinarians concluded in most cases grass eating is a common behavior in normal dogs and has no correlation with illness. Additionally, most dogs do not appear to routinely vomit after eating grass.

A study with cats shows that cats are less likely to eat plants than dogs. Just like dogs, most cats do not routinely show signs of illness prior to eating plants and don't regularly vomit afterward.

The researchers have hypothesized that plant eating may serve to help remove intestinal parasites from the gastrointestinal system of wild canids and felids. Our domesticated pets have simply inherited this instinct.

When faced with questions about plant-eating behavior, veterinarians should feel comfortable letting the clients know that this is usually normal for dogs and cats. I concur with this assumption. Today's domestic dog is not a true carnivore, meaning a meat eater only. Nor are cats and dogs true herbivores meaning only eating fibers and non-meat. Today's domestic dogs and cats are more correctly classified omnivores, meaning they eat meat and fiber and grains, much like the majority of the human population.

Personally, I often crave sweet corn on the cob — in fact I love it — but, as we are aware, most of the fiber of corn passes through the digestive tract rather quickly. I think dogs and cats crave grass as well, especially early in the spring after a winter if no access.

However, if a dog or cat is vomiting or sick and then eats grass, this will only make your pet sicker and more dehydrated. Because of that, a vomiting dog or cat should not be allowed grass access.

In fact, We have had to do exploratory surgery a number of times to remove a stomach blocked with grass, most often in dogs. This is most common in the obsessive/compulsive behavior seen in some dogs today.

This time of year, we must also be careful to never allow a pet to ingest cheatgrass or foxtails as the seeds are known to migrate and even perforate the intestinal tract.

So in general, I would have you discourage your pets from ingesting grass. And, of course, any pet with more than just the occasional spitting up or episode of vomiting (grass or not) should have a physical exam performed by your family veterinarian.

Dr. Darren Woodson has practiced veterinary medicine in the Farmington area for more than 28 years and has a passion for educating pet owners. If you have a question you would like him to address, email Please understand Dr. Woodson will choose the questions that are most relevant to our readers.